I. Field
The present invention relates generally to data communication, and more specifically to pilot and data transmission schemes for multi-antenna communication systems utilizing multi-carrier modulation.
II. Background
A multi-antenna communication system employs multiple (T) transmit antennas and one or more (R) receive antennas for pilot and data transmission. The T transmit antennas may be used to increase throughput by transmitting independent data streams from these antennas. The T transmit antennas may also be used to improve reliability by transmitting a single data stream redundantly from these antennas.
In a multi-antenna communication system, it may be necessary to estimate the channel gains between the T transmit antennas and the R receive antennas. The channel estimate may be needed to determine a particular mode to use for data transmission, to process a received data transmission, and so on. Channel estimation is typically performed by transmitting pilot symbols that are known a priori by the receiver. The receiver can then estimate the channel gains as the ratio of the received pilot symbols over the known pilot symbols.
Channel estimates obtained based on pilot transmission are normally impaired by both noise and interference. The noise can come from various sources, such as the wireless channel, receiver electronics, and so on. Noise impairment can typically be addressed by properly designing a pilot signal and/or transmitting the pilot signal for a sufficient period of time such that channel estimates of a particular desired quality can be obtained by the receiver.
For a multi-antenna system, the interference can result from transmitting the pilot signal simultaneously from all T transmit antennas. This is because the pilot signal transmitted from each antenna acts as interference to the pilot signals transmitted from the other antennas.
The same interference phenomenon occurs when the T transmit antennas are used for data transmission. In particular, if the same signal is redundantly transmitted from multiple antennas without addressing interference, then signal cancellation may occur at the receiver depending on the channel conditions and the specific location of the receiver. Consequently, greater throughput and/or reliability would not be achieved by the simultaneous transmission of data from multiple antennas.
There is therefore a need in the art for transmission schemes that can effectively address interference in multi-antenna communication systems.